Conventionally, outflow valves for controlling the volume of used air to be discharged out of a passenger aircraft body are controlled by closed loop controllers through unidirectional databuses. Each closed loop controller supplies a control signal or valve adjustment value through a separate databus to the respective outflow valve or valves. These valves are distributed along the length of the aircraft body and provide an air passage from the inside of the aircraft body to the atmosphere. In response to such a control the valves discharge regulated volumes of used air to the atmosphere. A further feedback databus is provided for each valve to provide feedback information regarding the current status of the respective valve to the closed loop controller.
Such a conventional system requires a total of eight databuses for each valve in the system. Four of one-way databuses connect two master controllers to two slave valve controllers and four one-way return databuses connect the slave valve controllers with master controllers, for supplying feedback information to the master controllers. In spite of this number of databuses, the conventional systems are not constructed to increase the reliability of the system. Moreover, each master controller can control only the outflow or air discharge valve to the slave controllers of which it is connected. Intercommunication between any master controller and any one of a plurality of slave valve controllers is conventionally not possible. Another drawback of such conventional systems is seen in that a two-way intercommunication between all components of the system is either not possible at all or at least economically not feasible.